Integrated circuitries or integrated circuits (ICs) are typically mounted in plastic packages to protect the sensitive integrated circuitries from environmental influences. However, mounting an integrated circuitry in a plastic package can exert considerable mechanical stress on the semiconductor material and thus on the semiconductor substrate of the integrated circuitry.
The mechanical stress or the mechanical strain present in the semiconductor material of the semiconductor substrate and acting on the integrated circuitry is generally hard to reproduce because the mechanical stress depends on the combination of the materials used for the semiconductor substrate and for the package and, in addition, on the packaging process of the integrated circuitry itself.
Thus, mechanical stress problems are caused by packaging, soldering, humidity changes in plastic packages, bending effects of the die (the semiconductor substrate), trench influences to neighboring devices, etc. The mechanical instabilities lead to current and voltage changes in reference circuits and to changes in passive components like on-chip inductors, capacitors and resistors and active components (e.g. transistors, diodes etc.) in the order of about 3% of the nominal value caused by stress or strain induced piezo-effects in the passive and active components, respectively.
To summarize, mechanical stress seems to be a lifetime effect, but actually 90% of the drift effects of the behavior of integrated circuits is caused by packaging, soldering, humidity, and temperature gradients on the die (i.e. the semiconductor substrate), as an expansion of a plastic package leads to the bending of the chip.
Thus, up to now only 1% to 3% accuracy and stability over lifetime and temperature range of integrated circuitries could be achieved, even with a trimming approach on a wafer.
Therefore, there is a need for improved integrated circuits which work with high precision and high lifetime stability combined with a very low temperature drift and low power or phase noise. Thus, accurate and inexpensive low-power or low-phase noise for on-chip oscillators without external components are required for many integrated circuits (ICs) with digital protocols or RF interfaces.